JPH11294212A - Fuel supply controller for by-fuel internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce NOx, HC, CO emitted from an engine. SOLUTION: An engine is provided with a CNG supply device 17 supplying CNG and a gasoline supply device 18 supplying gasoline. At normal operation only CNC is supplied to the engine while supply of gasoline is stopped. When a residual CNG amount is less than a lowest threshold, supply of CNG is stopped and supply of gasoline is started. Even when a CNG filling action is performed supply of CNG is not restarted, and when the residual gasoline amount is less than the lowest threshold supply of CNG is restarted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel supply control device for a bifuel internal combustion engine.

[0002]

2. Description of the Related Art In a bifuel internal combustion engine capable of supplying at least one of a gas fuel and a liquid fuel to an engine, gasoline is supplied to the engine during normal operation, and the supply of compressed natural gas (CNG) is stopped. 2. Description of the Related Art A bi-fuel internal combustion engine is known which supplies CNG to the engine and stops gasoline supply during high-load operation of the engine (see Japanese Utility Model Laid-Open No. 7-30344).

[0003]

[SUMMARY OF THE INVENTION However, in the preferred direction which is supplied to the engine to CNG than gasoline in order to reduce NO _X exhausted from the engine, HC, CO and the like, thus the above-mentioned bi-fuel internal combustion engine Supply only gasoline to the engine during normal operation,
G NO _X discharged from the temporarily performed so that the engine the supply of, HC, there is a problem that it is impossible to sufficiently reduce the like CO.

[0004]

According to the present invention, there is provided a bi-fuel internal combustion engine capable of supplying at least one of a gas fuel and a liquid fuel to an engine. The supply of the gas fuel and the supply of the liquid fuel are stopped, and the supply of the liquid fuel to the engine and the supply of the gas fuel are stopped when the remaining gas fuel amount becomes smaller than the lower threshold value. That is the normal supply of the liquid fuel is stopped during operation, NO _X exhausted from the engine because the gas fuel supplied to the engine,
HC, CO, etc. are sufficiently reduced.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is an engine body, 2 is a piston, 3 is a combustion chamber, 4 is an intake port, 5 is an intake valve, 6 is an exhaust port, 7 is an exhaust valve, and 8 is combustion. The ignition plugs arranged in the chamber 3 are respectively shown. The intake port 4 is connected to a surge tank 10 via an intake branch pipe 9, and the surge tank 10 is connected to an air cleaner 12 via an intake duct 11.
Connected to. A throttle valve 13 is provided in the intake duct 11.
Is arranged. On the other hand, the exhaust port 6 is connected to the exhaust manifold 1
4 is connected to a casing 16 containing a three-way catalyst 15.

The internal combustion engine shown in FIG. 1 includes a gas fuel supply device 17 and a liquid fuel supply device 18. The internal combustion engine shown in FIG. 1 uses CNG as gas fuel and gasoline as liquid fuel. Therefore, hereinafter, the gas fuel supply device will be referred to as CNG supply device, and the liquid fuel supply device will be referred to as gasoline supply device. The CNG supply device 17 includes a CNG injection valve 17a disposed in the intake branch pipe 9,
The CNG injection valve 17a is connected to a CNG cylinder 17c mounted on a vehicle via a CNG supply pipe 17b. Note that CN
A fuel cutoff valve and a regulator (not shown) are disposed in the G supply pipe 17b. Similarly, the gasoline supply device 18
Has a gasoline injection valve 18a arranged in the intake branch pipe 9, and this gasoline injection valve 18a
b, it is connected to the gasoline tank 18c mounted on the vehicle. A fuel pump (not shown) is arranged in the gasoline supply pipe 17b. The CNG injection valve 17a and the gasoline injection valve 18a are respectively connected to the electronic control unit 30
Is controlled based on the output signal from the controller.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, and always connected via a bidirectional bus 31. It has a B-RAM (backup RAM) 35, an input port 36, and an output port 37 connected to a power supply. A pressure sensor 38 for generating an output voltage proportional to the absolute pressure PM in the surge tank 10 is attached to the surge tank 10. An air-fuel ratio sensor 39 is attached to the exhaust manifold 14. CNG supply pipe 1
A CNG amount sensor 40 for generating an output voltage proportional to the remaining CNG amount VC in the CNG cylinder 17c is disposed in the gas tank 7c.
A gasoline amount sensor 41 for generating an output voltage proportional to the remaining gasoline amount VG in the inside is provided. These sensors 3
The output voltages of 8, 39, 40 and 41 correspond to the corresponding A
The data is input to the input port 36 via the D converter 42. The input port 36 is connected to a rotation speed sensor 43 that generates an output pulse indicating the engine rotation speed N. On the other hand, the output port 37 is connected to the ignition plug 8, the CNG fuel injection valve 17a, and the gasoline injection valve 18a via the corresponding drive circuits 44, respectively.

In the internal combustion engine shown in FIG. 1, the CNG injection time TAUC and the gasoline injection time TAU are calculated based on the following equations, for example.
G is calculated respectively. TAUC = TAUCB / KC / FAF / (1-m) TAUG = TAUGB / KG / FAF / m where TAUCB is the basic CNG injection time and KC is CNG.
Correction coefficient, FAF is a feedback correction coefficient, m is a supplied fuel control coefficient, TAUGB is a basic gasoline injection time, K
G represents a gasoline correction coefficient.

The basic CNG injection time TAUCB is set to C
When only NG is supplied, the surge tank 10 indicates the engine operating state, that is, the engine load, for example, the CNG injection time required by an experiment to obtain the target air-fuel ratio, that is, the stoichiometric air-fuel ratio. Absolute pressure PM
Are stored in the ROM 32 in advance in the form of a map shown in FIG. 2 as a function of the engine speed N and the engine speed N.

The CNG correction coefficient KC is a warm-up increase correction coefficient, an acceleration increase correction coefficient, and a CN when supplying CNG to the engine.
It is a collective representation of the G composition correction coefficients and the like. If no correction is required, KC = 1. The basic gasoline injection time TAUGB is a gasoline injection time obtained by an experiment which is necessary in advance to make the air-fuel ratio a stoichiometric air-fuel ratio when only gasoline is supplied to the engine. Absolute pressure P
It is stored in the ROM 32 in advance in the form of a map shown in FIG. 3 as a function of M and the engine speed N.

The gasoline correction coefficient KG is a collective representation of a warm-up increase correction coefficient, an acceleration increase correction coefficient, and the like when gasoline is supplied to the engine. If no correction is required, KG = 1. Become. The feedback correction coefficient FAF is for making the actual air-fuel ratio coincide with the stoichiometric air-fuel ratio based on the output signal of the air-fuel ratio sensor 39.
It fluctuates around 1.0.

The supplied fuel control coefficient m is for controlling the fuel supplied to the engine. When m = 0, the gasoline injection time TAUG becomes zero, as can be seen from the above formula, so that CNG is supplied to the engine and the supply of gasoline is stopped. When m = 1.0, CNG injection time T
Since AUC becomes zero, gasoline is supplied to the engine and C
The supply of NG is stopped. When 0 <m <1.0, both CNG and gasoline are supplied to the engine, and gasoline is supplied by m for the total fuel amount to be supplied to the engine.

Next, a method for controlling the fuel supply to the internal combustion engine of FIG. 1 will be described with reference to FIG. During normal operation, such as at time a in FIG. 4, the supplied fuel control coefficient m is maintained at zero. That is, only CNG is supplied to the engine during normal operation, and the supply of gasoline is stopped. Preferably better to supply the CNG than gasoline engines in order to reduce the so NO _X exhausted from the engine, HC, CO and the like mentioned in the introduction, thus supplying CNG to only this way the engine during normal operation discharged from the engine in the majority of the engine operating condition when such that NO _X, so that it is possible to reduce HC, CO and the like.

In this case, the residual CNG amount VC gradually decreases, while the residual gasoline amount VG is kept constant. Next, when the remaining CNG amount VC becomes smaller than the lower threshold value VCL as in the time b, the supply fuel control coefficient m is changed to 1.0. That is, C to the engine
The supply of NG is stopped, and only gasoline is supplied to the engine. As a result, the fuel supply to the engine is continuously performed.
When VC <VCL, for example, a warning device may be activated to notify the vehicle driver that the CNG filling operation should be performed.

Next, even when the residual CNG amount VC becomes larger than the fixed value VC1 as at time c, that is, CN
Even when the G filling operation is performed, the supplied fuel control coefficient m is maintained at 1.0, that is, the supply of CNG to the engine is continuously stopped, and only gasoline is continuously supplied. In this case, the remaining gasoline amount VG gradually decreases, while the remaining CNG amount VC is kept constant. Next, as at time d, the remaining gasoline amount VG is reduced to the lower threshold VGL.
If it becomes smaller, the supplied fuel control coefficient m is changed to a small constant value mm, for example, 0.1, that is, the supply of CNG to the engine is restarted, and the supply of gasoline is continued. That is, in this case, both CNG and gasoline are supplied to the engine, and most of the fuel supplied to the engine at this time is CNG. When VG <VGL, for example, a warning device may be activated to notify the vehicle driver that gasoline refueling should be performed.

Next, when the remaining gasoline amount VG becomes larger than the fixed value VG1 as at time e, that is, when the gasoline refueling operation is performed, the supply fuel control coefficient m is changed to zero again. That is, the supply of gasoline to the engine is stopped again, and only CNG is supplied. As described above, in the internal combustion engine shown in FIG.
The supply of NG is not restarted immediately, but the supply of gasoline to the engine is continued until the gasoline refueling operation is performed. In other words, once the gasoline supply to the engine is started, the gasoline supply to the engine is continuously performed until the gasoline refueling operation is performed. This is done for the following reasons.

That is, when the CNG charging operation is performed, the supply of CNG to the engine is immediately restarted, and the supply of gasoline is stopped.
Is supplied only during a period from the time when the pressure becomes lower than the lower limit threshold value VCL until the CNG filling operation is performed, a certain amount of gasoline remains in the gasoline tank 17c during normal operation. . This remaining gasoline is not consumed until the remaining CNG amount VC becomes lower than the lower threshold value VCL again, and therefore the gasoline is stored in the gasoline tank 17c for a long period of time, so that the gasoline is deteriorated and the gasoline injection valve 18a or the fuel pump is turned off. It may become inoperable.

Therefore, in the internal combustion engine shown in FIG. 1, once the gasoline supply to the engine is started, the gasoline supply to the engine is continuously performed until the gasoline refueling operation is performed. In particular, the remaining gasoline amount VG has a lower limit. The supply of gasoline is continued even after the value becomes lower than the value VGL. As a result, gasoline is stored in gasoline tank 17c.
For a long period of time. Therefore, the gasoline can be prevented from being deteriorated, and the gasoline injection valve 18a or the fuel pump can be prevented from becoming inoperable.

When gasoline is consumed from a state in which the gasoline tank 17c is almost completely filled with gasoline, an air layer is formed in the gasoline tank 17c above the gasoline level, and as a result, a large amount of gasoline vapor is generated. Can occur. However, in the internal combustion engine shown in FIG. 1, once gasoline supply to the engine is started, gasoline supply to the engine is continued until gasoline refueling is performed, so that an air layer is formed in the gasoline tank 17c. It is possible to shorten the period from when the gasoline tank 17c is filled with gasoline to the gasoline tank 17c again.
Therefore, the gasoline vapor generation amount can be reduced. Further, since the supply of gasoline is continued even after the remaining gasoline amount VG becomes smaller than the lower threshold value VGL, the gasoline vapor generation source is reduced, and therefore the gasoline vapor generation amount can be further reduced. .

FIGS. 5 and 6 show a routine for executing the above-described supply fuel control. This routine is executed by interruption every predetermined set time. Referring to FIGS. 5 and 6, first, at step 50, it is determined whether or not the two-fuel flag is set. The two-fuel flag is set when both CNG and gasoline are to be supplied to the engine, and is reset when one of CNG and gasoline is to be supplied to the engine. Since the 2 fuel flag is normally reset, the process proceeds from step 50 to step 51, where it is determined whether or not the gasoline flag is set. This gasoline flag is set when gasoline is to be supplied to the engine, and is reset when gasoline supply is to be stopped. Since the gasoline flag is normally reset, the process proceeds from step 51 to step 52, where the supplied fuel control coefficient m is set to zero. That is, during normal operation in which both the two-fuel flag and the gasoline flag are reset, only CNG is supplied to the engine. In a succeeding step 53, it is determined whether or not the remaining CNG amount VC is smaller than a lower threshold value VCL. When VC ≧ VCL, the processing cycle ends. When VC <VCL, the routine proceeds to step 54, where the gasoline flag is set, and the processing cycle ends.

When the gasoline flag is set, the routine proceeds from step 51 to step 55, where the supplied fuel control coefficient m is set to 1.0. That is, when the gasoline flag is set, the supply of CNG to the engine is stopped, and only gasoline is supplied. In the following step 56, it is determined whether or not the remaining gasoline amount VG is smaller than the lower threshold value VGL. When VG ≧ VGL, the processing cycle ends. When VG <VGL, the routine proceeds to step 55, where it is determined whether or not the remaining CNG amount VC is larger than the fixed amount VC1, that is, whether or not the CNG filling operation has been performed. When VC ≦ VC1, it is determined that the CNG filling operation has not been performed yet, and the processing cycle ends. On the other hand, when VC> VC1, it is determined that the CNG filling operation has been performed, and then the routine proceeds to step 58, where the two-fuel flag is set, and the processing cycle ends.

2 When the fuel flag is set, the process proceeds from step 50 to step 59, where the supplied fuel control coefficient m
Is set to a small constant value mm. That is, when the two-fuel flag is set, a large amount of CNG and a small amount of gasoline are supplied simultaneously. In the following step 60, it is determined whether or not the remaining gasoline amount VG is larger than a fixed value VG1. V
When G ≦ VG1, it is determined that the gasoline refueling operation has not been performed yet, and the processing cycle ends. VG> VG
In the case of 1, it is determined that the gasoline refueling action has been performed, and then the routine proceeds to step 61, where the 2 fuel flag is reset,
In the following step 62, the gasoline flag is reset, and then the processing cycle ends. That is, the supply of gasoline to the engine is stopped, and only CNG is supplied.

FIG. 7 shows a routine for calculating the above-described fuel injection time. This routine is executed by interruption every predetermined set crank angle. Referring to FIG. 7, first, at step 70, the basic CNG injection time TAUCB is calculated using the map of FIG. 2, and at the subsequent step 71, the basic gasoline injection time TAUGB is calculated using the map of FIG. In a succeeding step 72, a CNG correction coefficient KC is calculated, and in a succeeding step 73, a gasoline correction coefficient KG is calculated. Subsequent step 74
Then, the feedback correction coefficient FAF is calculated. In the following step 75, the CNG injection time TAUC is calculated based on the following equation using the supplied fuel control coefficient m calculated in the routine of FIGS.

TAUC = TAUCB · KC · FAF · (1-m) Each CNG injection valve 17a performs CNG injection by TAUC only. In the following step 76, the gasoline injection time TAUG is calculated based on the following equation using the supplied fuel control coefficient m calculated in the routine of FIGS. TAUG = TAUGB / KG / FAF / m In each gasoline injection valve 18a, gasoline is injected only by TAUG.

In the embodiments described above, CNG is used as the gas fuel and gasoline is used as the liquid fuel. However, natural gas and petroleum gas which are primary fuels such as liquefied petroleum gas (LPG), or coal conversion gas and petroleum conversion gas which are secondary fuels can be used as the gas fuel. As the liquid fuel, hydrocarbons such as isooctane, hexane, heptane, light oil, and kerosene, or hydrocarbons such as butane and propane that can be stored in a liquid state, or methanol can be used.

[0026]

Supply of the normal liquid fuel during operation according to the present invention is stopped, since the gas fuel supplied to the engine NO _X exhausted from the engine, HC, CO and the like can be sufficiently reduced.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a basic CNG injection time.

FIG. 3 is a diagram showing a basic gasoline injection time.

FIG. 4 is a time chart for explaining a supply fuel control method.

FIG. 5 is a flowchart for executing a supply fuel control method.

FIG. 6 is a flowchart for executing a supply fuel control method.

FIG. 7 is a flowchart for calculating a fuel injection time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine main body 9 ... Intake branch pipe 17 ... CNG supply device 17c ... CNG cylinder 18 ... Gasoline supply device 40 ... CNG amount sensor

Claims (1)

[Claims] In a bifuel internal combustion engine capable of supplying at least one of a gas fuel and a liquid fuel to an engine, during normal operation, the gas fuel is supplied to the engine and the supply of the liquid fuel is stopped. A supply fuel control device for a bi-fuel internal combustion engine, wherein liquid fuel is supplied to the engine and supply of gas fuel is stopped when the amount becomes smaller than a lower threshold.